Call Function when User Types Certain Keyword - vb.net

Question

Okay, so I am working on a small scripting language using a VB Console Application.
I want the user to input "say('something')" and it calls the function I made named "say", is there a way to call the function and still use the following code:
Module Module1
Sub say(sayline)
Console.WriteLine(sayline)
End Sub
Sub Main()
Dim cmd As String
Console.WriteLine(">")
Do
Console.Write("")
cmd = Console.ReadLine()
If cmd IsNot Nothing Then cmd
Loop While cmd IsNot Nothing
End Sub
End Module

Answer 1

No, you cannot just call a method from user's string. You need to interpret the entered data.
First, you need to split your method name and arguments so that entered "say('something')" will transform to say and something. Remember that user can enter wrong data and you need to check if this call is correct - it's all about syntactic and lexical analysis. I hope you understand how to do this because it is pretty difficult.
Then, you need to check if you have a method called say. In case of plain and simple structure, switch construction will be enough. If your have such method, then pass something argument to this method. Else, output something like "unknown method".

Answer 2

If you wanted to call the method say upon typing the word say(something) and display the word something, then you can just have a certain condition that if the user types the word say within the input then call say method else, do whatever you want to do under else portion. Parse the input and omit the word say from the input and display it then.
You can have your code this way for example. (I just copied your code and added some codes to meet what you wanted... in my understanding)
Module Module1
Sub say(ByVal sayline)
Console.WriteLine(sayline)
End Sub
Sub Main()
Dim cmd As String
Do
Console.Write("> ")
cmd = Console.ReadLine()
Try
If cmd IsNot Nothing And cmd.Substring(0, 3).ToUpper().Equals("SAY") Then
say(parseInput(cmd))
End If
Catch ex As Exception
Console.WriteLine("message here")
End Try
Loop While cmd IsNot Nothing
End Sub
Function parseInput(ByVal cmd As String) As String
Dim input As String = ""
For index As Integer = 3 To cmd.Length - 1
If Char.IsLetter(cmd) Then
input += cmd.Substring(index, 1)
Else
input = input
End If
Next
Return input
End Function
End Module